In process automation technology, especially for automation of chemical processes or procedures for producing a product from a raw or starting material by the use of chemical, physical or biological processes and/or for control of industrial plants, measuring devices installed near to the process, so-called field devices, are applied. Field devices embodied as sensors can monitor, for example, process measurement variables, such as pressure, temperature, flow, fill level or measured variables of liquid- and/or gas analysis, such as, for example, pH-value, conductivity, concentrations of certain ions or chemical compounds and/or concentrations or partial pressures of gases.
Used in a process installation are frequently a large number of the most varied of sensors. A sensor arranged at a certain location of installation in a process, for example, a sensor installed at a certain location of installation, and embodied for registering one or more measured variables, forms together with a measurement transmitter (which also may be referred to just as the transmitter for short) a measuring point.
A sensor includes, as a rule, a measuring transducer, which is embodied to register the measured variable to be monitored and to produce an electrical measurement signal correlated with the current value of the measured variable. Serving for additional processing of the measurement signal is an electronic circuit, which is embodied to condition the electrical measurement signal further, for example, to digitize it, and to convert it into a measured value of the measured variable and/or into a variable derived from the measured value, and, in given cases, to output such to a superordinated unit. The circuit can include, besides the measured value formation and measured value forwarding, more extensive functions. For example, it can be embodied to perform a more extensive evaluation of the measured values or to perform sensor diagnostics, in the case of which a current state of the sensor is determined and/or a prediction made of the remaining life of the sensor. The circuit can be arranged entirely or partially in the transmitter.
In the case of sensors of the aforementioned type, the particular circuit is frequently connected with a superordinated data processing system, which is arranged most often spatially removed from the respective measuring point and to which the measured values produced by the respective sensor, diagnostically relevant data or other sensor data are forwarded. The superordinated data processing system can especially comprise one or more electronic, process controllers, for example, one or more measurement transmitters installed on-site, a process control computer, computers at a control station or a programmable logic controller (PLC).
Serving frequently for data transmission in such industrial measuring arrangements, at least sectionally, are fieldbus systems, such as, for example, FOUNDATION Fieldbus, PROFIBUS, ModBus, etc. or, for example, also networks based on the Ethernet standard, as well as the corresponding, most often application independent, standardized, transmission protocols.
Known from Published International Application WO 2005/031339 is a liquid sensor, which is connected via a coupling with a measurement transmitter and further with a superordinated data processing system. The sensor includes a measuring transducer and a sensor circuit, which has a preprocessing circuit for preprocessing the analog measurement signals produced by means of the measuring transducer, an analog/digital converter for converting the registered analog measurement signals into digital measurement signals and a first interface for transmitting the digital measurement signals to the superordinated measurement transmitter. The coupling includes a sensor side, primary coupling element and a thereto complementary, secondary coupling element, which is connected with the measurement transmitter. The first interface is embodied to transfer the digital measurement signals via the coupling to the measurement transmitter. The secondary coupling element includes another electronic circuit, which has a second interface complementary to the first interface, which is embodied to receive the measuring signals transmitted from the first interface. The second interface can, moreover, transmit data as well as energy via the coupling to the first interface of the sensor. The transmission of energy and data occurs in the case of the sensor known from WO 2005/031339 contactlessly by means of an inductive coupling of the first and second interfaces. This assures also a galvanic decoupling of the sensor from the measurement transmitter.
Measurement transmitters conventionally have display means, e.g. a display, and input means, e.g. in the form a keyboard or one or more rotate/press switches, by means of which a user can interact with the measurement transmitter, i.e. read measured values and sensor data, respectively input parameters or commands.
More recently, measuring arrangements have become known, which do without a conventional measurement transmitter equipped with the input- and display means. Described in German Patent DE 10 2011 107 717 is a sensor for liquid- or/and gas analysis, which is connected with a measuring- or/and transmitter circuit, respectively with a superordinated control system. The sensor includes a sensor housing, in which circuit means for registering, conditioning and forwarding measured values to the measuring- or/and transmitter circuit, respectively to the control system, are provided. This circuit means includes an analog sensor electronics, an analog/digital converter for converting the registered analog, measured values into digital, measured values, a calculating unit and communication means for preparing and forwarding the digital, measured values to the measuring- or/and transmitter circuit, respectively to the control system, according to a standard communication protocol of process technology, for example, a HART, PROFIBUS PA, PROFIBUS DB or Foundation Fieldbus protocol. Goal of the sensor construction illustrated in DE 10 2011 107 717 is to integrate as much of the electronics as possible into the sensor. Thus, the sensor electronics arranged in the sensor housing serves not only for registering and, in given cases, digitizing the measured values registered by a measuring transducer of the sensor, but also for additional processing and conversion of the measured values into a standard communication protocol usable by the control station.
Sensors used for liquid- and/or gas analysis must, as a rule, from time to time during their lifetime, undergo maintenance, especially be calibrated or regenerated. To this end, frequently the sensor to be maintained is removed from the measuring point and the maintenance measure performed at another site, for example, in the laboratory. In the intervening times, the measuring point can be operated further with another sensor of the same type. The lifetime of sensors for liquid- and/or gas analysis is, moreover, limited, depending on the particular features of the measuring point, and can extend, for example, from few days to a number of months. This leads to the fact that the sensors of a measuring point must regularly be replaced. A disadvantage of a measuring arrangement, wherein as much electronics as possible is accommodated in the sensor, is that, in the case of each sensor replacement, not only data stored in the sensor, but also measuring point specifically adapted parameters and measuring location specific program code get removed from the measuring point along with the sensor that is being replaced. These parameters, respectively such program code, must each time be made available to the replacement sensor.
The terminology “parameter” means herein an actuating- or influencing variable, which affects the sensor and, thus, changes the behavior of the sensor or delivers information concerning the state of the sensor.